Document the valid values of required contact point nr

[ignasi35]

REQUIRED_CONTACT_POINT_NR is set on the deployment YAML file to "3". We could specify it must be equal or less than the replica number, otherwise the relation between the two values is not clear.

https://github.com/lagom/shopping-cart-scala/blob/e30b41723922ed635a8c072ea138262147a69cea/shopping-cart-impl/src/main/resources/prod-application.conf#L36

[TimMoore]

It's probably worth copying comments from the original reference.conf for any properties in the example configuration:

https://github.com/akka/akka-management/blob/7b2892fa7a616c815541d49647555d93a52b4a69/cluster-bootstrap/src/main/resources/reference.conf#L86-L89

      # The smallest number of contact points that need to be discovered before the bootstrap process can start.
      # For optimal safety during cluster formation, you may want to set these value to the number of initial
      # nodes that you know will participate in the cluster (e.g. the value of `spec.replicas` as set in your kubernetes config.
      required-contact-point-nr = 2

[ignasi35]

Both in this issue and a few others with a similar comment from @TimMoore, I think that at least a link to the original reference.conf (instead of copy/pasting comments) could be enough.

Adding the link (instead of copying the comment) has the advantage of guiding the user into a wider range of information.